The present invention relates to the fabrication of microelectronic and micro-electromechanical devices.
Photomasks used in the fabrication of microelectronic and micro-electromechanical devices, e.g., integrated circuits (“chips”), wafers, and substrates used to interconnect chips typically are required to be free of defects. In photomasks (“masks”) used to pattern features of microelectronic substrates (e.g., transistors, micro-electromechanical (“MEMS”) devices, and other small devices), it is becoming increasingly difficult to meet this requirement. The costs and amount of time required to fabricate a mask, as well as the number of masks in a set of masks are increasing dramatically, particularly in advanced semiconductor technologies. The layouts to be patterned by a mask are becoming increasingly complex, containing ever greater numbers of features, while the sizes of such features (e.g., the widths and lengths of lines) shrink with a ground rule that is reduced with succeeding generations of technology.
Unfortunately, it is increasingly difficult to produce photomasks to the requirements of increased complexity and reduced ground rule, such that many photomasks are defective as fabricated. Current practice requires that defective photomasks either be repaired or replaced with photomasks which do not have defects. However, since the repair of masks and the manufacture of new masks require expenditures of both time and money, efforts to address such defects can be costly at the introduction of a new product and can even sometimes hinder its entry into the market.